Experimental and computational mediated illustration of effect of different substituents on adsorption tendency of phthalazinone derivatives on mild steel surface in acidic medium

Four 1-(2H)-phthalazinone substituted compounds were investigated for their anticorrosion potentials on mild steel in 1 M HCl using electrochemical techniques, namely Tafel polarization and impedance spectroscopy. Fourier Transform Infrared (FTIR) spectroscopic technique was used to substantiate the interaction of the phthalazinone molecules with mild steel. Potentiodynamic polarization study suggested that inhibitor compounds exhibited mixed-type corrosion inhibition activities by repressing both oxidative steel dissolution and reductive hydrogen evolution reactions. Adsorption of the phthalazinone molecules on mild steel surface was modeled in Monte Carlo simulations. AC impedance spectroscopy measurements revealed that the corrosion of mild steel in the studied electrolytes is driven by single charge transfer mechanism and the studied phthalazinone molecules reduced the steel dissolution by forming adsorbed pseudo-capacitive film on the steel surface. Scanning electron microscopy plates showed the protective effects of the inhibitor molecules. The inhibition efficiencies of the studied phthalazinone molecules followed the order, P3 (78.25%) > P1 (77.24%) > P2 (76.60%) > P4 (67.86%) at 500 ppm. Both quantum chemical calculations and Monte Carlo simulations corroborated experimental results.